All but the simplest of electronic devices utilize nonvolatile memories. When an electronic device must retain information during and after being placed in an unpowered state, nonvolatile memories must be provided. Several types of nonvolatile memories are known in the art. Nonvolatile memories may be portable, auxiliary, or integrated in a circuit or as a component in both general and embedded computer systems. Most generally, nonvolatile memories are found in digital cameras, cellular telephones, music players, and as the key component in portable memory devices such as USB based flash drives.
Nonvolatile memory is often formed using electrically-erasable programmable read only memory (EPROM) technology. EPROM, also known as flash memory, uses an architecture that is inadequate in its access, erase and write times for the rapidly increasing operational speed requirements and rapidly decreasing size requirements of electronic devices. What is needed is memory architecture with faster access, erase and write times scalable to smaller devices. Volatile memories (such as Random Access Memory (RAM)) can potentially be replaced by nonvolatile memories if the speeds of nonvolatile memories are increased to meet the requirements for RAM and other applications currently using volatile memories. Resistive switching memories may provide an alternative to flash memories.
Resistive switching nonvolatile memories are formed of arrays of resistive switching elements where each element has two or more stable resistive states. Bi-stable resistive switching elements have two stable states. The application of an electric field having a particular voltage or current will result in a desired element resistance. Voltage pulses are typically used to switch the memory element from one resistance state to the other.
Resistive switching elements use a “forming process” to prepare a memory device for use. The forming process is typically applied at the factory, at assembly, or at initial system configuration. A resistive switching material is normally insulating, but a sufficient voltage (known as a forming voltage) applied to the resistive switching material will form one or more conductive pathways in the resistive switching material. Through the appropriate application of various voltages (e.g. a set voltage and reset voltage), the conductive pathways may be modified to form a high resistance state or a low resistance state. For example, a resistive switching material may change from a first resistivity to a second resistivity upon the application of a set voltage, and from the second resistivity back to the first resistivity upon the application of a reset voltage.
Resistive switching memory uses peripheral transistors to control the application of voltage to the resistive switching material, and thereby alter the resistive state of the resistive switching material. Resistive switching memory with a high forming voltage requires high voltage peripheral transistors. High voltage peripheral transistors add to the cost and complexity of the resistive switching memory. Consequently, a resistive switching memory with reduced forming voltage is desired.
One method for reducing forming voltage in resistive switching memory includes doping resistive switching elements with a dopant to increase the propensity of the resistive switching elements to form conductive pathways by creating electronic defects in the resistive switching element. One doping scheme includes depositing a dielectric host metal precursor during one cycle of an atomic layer deposition process, oxidizing the dielectric host metal precursor, and then depositing a dopant during a subsequent cycle of the atomic layer deposition process. This methodology results in a resistive switching element with doped and undoped layers of host metal oxide or nano-laminates. The nano-laminates do not provide adequate electronic defect density for ideal electron transport through the metal oxide/insulator. What is needed is a method for embedding dopant throughout the metal oxide or in an area of the metal oxide near one or more of the electrodes to improve defect density and improve switching behavior of the host metal oxide.